fn main() {
    let mut x = "升龙拳";
    println!("main的fn{}", x);
    x = "波动拳";
    println!("main的fn{}", x);
    const THREE_HOURS_SECONDS: u32 = 60 * 60 * 30;
    println!("THREE_HOURS_SECONDS{}", THREE_HOURS_SECONDS);
    num();
}
fn num() {
    let x = 5;
    let x = x + 1;
    {
        let x = x * 2;
        println!("num内部的x{}", x);
    }
    println!("num的x{}", x);
    let space = "     ";
    let space = space.len();
    println!("space{}", space);
}
